You have just asked to get a pickup into your dads life. Mini pickup? Cowboy Cadillac? Work truck? Monster Truck?
The Callaway Big Bertha has been around since the 80s. Probably the biggest model name in golf history, unless you count "eye" as a model name.
If there is a right answer here... Ask him for more details, there have been probably 100s of models with a version of that name.
If not...
If he's looking for a classic club, the Big Bertha Warbird, Hawk Eye, and The Great Big Bertha are probably the most iconic and some of the most influential clubs of all time. Still playable today.
Assuming though that he’s in his 70s, he’s probably looking for more distance or control, and therefore more modern.
And there I’m not much help on the specific models but… look up the model names and anything from 2018 (or realistically 2015) or later is going to be pretty close to the current technology.
For shaft, for a guy in his 70s, stay away from steel; stick with graphite.
I would like to say stick with regular shafts, but that depends… is he a former college golfer who still plays every week and chips wood every day? Then he’d be in a stiff shaft. My dad, a former hockey player, still had a 100mph + swing speed into his 60s. That put him on the edge of stiff and extra stiff… and he wasn’t particularly active anymore, though not in bad shape.
On the other hand, if he is swinging like Mr. and Mrs. Havercamp in Caddyshack, get an “A” flex shaft, which is senior flex.
What is your budget? New or used? Do you know what his current setup is and what he’s trying to improve? How far does he hit his driver? Slice draw or straight? Is this going to be hit off the tee or just fairway or both? He meant wood and not hybrid, right?